Wehavenowonlytomentiontheturkey-buzzardVulturaura，andtheGallinazo。Theformerisfoundwhereverthecountryismoderatelydamp，fromCapeHorntoNorthAmerica。DifferentlyfromthePolyborusBrasiliensisandChimango，ithasfounditswaytotheFalklandIslands。Theturkey-buzzardisasolitarybird，oratmostgoesinpairs。Itmayatonceberecognisedfromalongdistance，byitslofty，soaring，andmostelegantflight。ltiswellknowntobeatruecarrion-feeder。OnthewestcoastofPatagonia，amongthethickly-woodedisletsandbrokenland，itlivesexclusivelyonwhattheseathrowsup，andonthecarcassesofdeadseals。Wherevertheseanimalsarecongregatedontherocks，therethevulturesmaybeseen。TheGallinazoCathartesatratushasadifferentrangefromthelastspecies，asitneveroccurssouthwardoflat。41degs。Azarastatesthatthereexistsatraditionthatthesebirds，atthetimeoftheconquest，werenotfoundnearMonteVideo，butthattheysubsequentlyfollowedtheinhabitantsfrommorenortherndistricts。AtthepresentdaytheyarenumerousinthevalleyoftheColorado，whichisthreehundredmilesduesouthofMonteVideo。
ItseemsprobablethatthisadditionalmigrationhashappenedsincethetimeofAzara。TheGallinazogenerallyprefersahumidclimate，orrathertheneighbourhoodoffreshwater；henceitisextremelyabundantinBrazilandLaPlata，whileitisneverfoundonthedesertandaridplainsofNorthernPatagonia，exceptingnearsomestream。ThesebirdsfrequentthewholePampastothefootoftheCordillera，butIneversaworheardofoneinChile；inPerutheyarepreservedasscavengers。Thesevulturescertainlymaybecalledgregarious，fortheyseemtohavepleasureinsociety，andarenotsolelybroughttogetherbytheattractionofacommonprey。
Onafinedayaflockmayoftenbeobservedatagreatheight，eachbirdwheelingroundandroundwithoutclosingitswings，inthemostgracefulevolutions。Thisisclearlyperformedforthemerepleasureoftheexercise，orperhapsisconnectedwiththeirmatrimonialalliances。
Ihavenowmentionedallthecarrion-feeders，exceptingthecondor，anaccountofwhichwillbemoreappropriatelyintroducedwhenwevisitacountrymorecongenialtoitshabitsthantheplainsofLaPlata。
Inabroadbandofsand-hillockswhichseparatetheLagunadelPotrerofromtheshoresofthePlata，atthedistanceofafewmilesfromMaldonado，Ifoundagroupofthosevitrified，siliceoustubes，whichareformedbylightningenteringloosesand。ThesetubesresembleineveryparticularthosefromDrigginCumberland，describedintheGeologicalTransactions。[10]Thesand-hillocksofMaldonadonotbeingprotectedbyvegetation，areconstantlychangingtheirposition。Fromthiscausethetubesprojectedabovethesurface，andnumerousfragmentslyingnear，showedthattheyhadformerlybeenburiedtoagreaterdepth。Foursetsenteredthesandperpendicularly：byworkingwithmyhandsItracedoneofthemtwofeetdeep；andsomefragmentswhichevidentlyhadbelongedtothesametube，whenaddedtotheotherpart，measuredfivefeetthreeinches。Thediameterofthewholetubewasnearlyequal，andthereforewemustsupposethatoriginallyitextendedtoamuchgreaterdepth。Thesedimensionsarehoweversmall，comparedtothoseofthetubesfromDrigg，oneofwhichwastracedtoadepthofnotlessthanthirtyfeet。
Theinternalsurfaceiscompletelyvitrified，glossy，andsmooth。A
smallfragmentexaminedunderthemicroscopeappeared，fromthenumberofminuteentangledairorperhapssteambubbles，likeanassayfusedbeforetheblowpipe。Thesandisentirely，oringreaterpart，siliceous；butsomepointsareofablackcolour，andfromtheirglossysurfacepossessametalliclustre。Thethicknessofthewallofthetubevariesfromathirtiethtoatwentiethofaninch，andoccasionallyevenequalsatenth。
Ontheoutsidethegrainsofsandarerounded，andhaveaslightlyglazedappearance：Icouldnotdistinguishanysignsofcrystallization。InasimilarmannertothatdescribedintheGeologicalTransactions，thetubesaregenerallycompressed，andhavedeeplongitudinalfurrows，soascloselytoresembleashrivelledvegetablestalk，orthebarkoftheelmorcorktree。Theircircumferenceisabouttwoinches，butinsomefragments，whicharecylindricalandwithoutanyfurrows，itisasmuchasfourinches。
Thecompressionfromthesurroundingloosesand，actingwhilethetubewasstillsoftenedfromtheeffectsoftheintenseheat，hasevidentlycausedthecreasesorfurrows。Judgingfromtheuncompressedfragments，themeasureorboreofthelightningifsuchatermmaybeusedmusthavebeenaboutoneinchandaquarter。AtParis，M。HachetteandM。Beudant[11]succeededinmakingtubes，inmostrespectssimilartothesefulgurites，bypassingverystrongshocksofgalvanismthroughfinely-powderedglass：whensaltwasadded，soastoincreaseitsfusibility，thetubeswerelargerineverydimension，Theyfailedbothwithpowderedfelsparandquartz。Onetube，formedwithpoundedglass，wasverynearlyaninchlong，namely。982，andhadaninternaldiameterof。019ofaninch。WhenwehearthatthestrongestbatteryinPariswasused，andthatitspoweronasubstanceofsucheasyfusibilityasglasswastoformtubessodiminutive，wemustfeelgreatlyastonishedattheforceofashockoflightning，which，strikingthesandinseveralplaces，hasformedcylinders，inoneinstanceofatleastthirtyfeetlong，andhavinganinternalbore，wherenotcompressed，offullaninchandahalf；
andthisinamaterialsoextraordinarilyrefractoryasquartz！
Thetubes，asIhavealreadyremarked，enterthesandnearlyinaverticaldirection。One，however，whichwaslessregularthantheothers，deviatedfromarightline，atthemostconsiderablebend，totheamountofthirty-threedegrees。Fromthissametube，twosmallbranches，aboutafootapart，weresentoff；onepointeddownwards，andtheotherupwards。Thislattercaseisremarkable，astheelectricfluidmusthaveturnedbackattheacuteangleof26degs。，tothelineofitsmaincourse。BesidesthefourtubeswhichIfoundvertical，andtracedbeneaththesurface，therewereseveralothergroupsoffragments，theoriginalsitesofwhichwithoutdoubtwerenear。Alloccurredinalevelareaofshiftingsand，sixtyyardsbytwenty，situatedamongsomehighsand-hillocks，andatthedistanceofabouthalfamilefromachainofhillsfourorfivehundredfeetinheight。Themostremarkablecircumstance，asitappearstome，inthiscaseaswellasinthatofDrigg，andinonedescribedbyM。RibbentropinGermany，isthenumberoftubesfoundwithinsuchlimitedspaces。AtDrigg，withinanareaoffifteenyards，threewereobserved，andthesamenumberoccurredinGermany。InthecasewhichIhavedescribed，certainlymorethanfourexistedwithinthespaceofthesixtybytwentyyards。Asitdoesnotappearprobablethatthetubesareproducedbysuccessivedistinctshocks，wemustbelievethatthelightning，shortlybeforeenteringtheground，dividesitselfintoseparatebranches。
TheneighbourhoodoftheRioPlataseemspeculiarlysubjecttoelectricphenomena。Intheyear1793，[12]oneofthemostdestructivethunderstormsperhapsonrecordhappenedatBuenosAyres：thirty-sevenplaceswithinthecitywerestruckbylightning，andnineteenpeoplekilled。
Fromfactsstatedinseveralbooksoftravels，Iaminclinedtosuspectthatthunderstormsareverycommonnearthemouthsofgreatrivers。Isitnotpossiblethatthemixtureoflargebodiesoffreshandsaltwatermaydisturbtheelectricalequilibrium？EvenduringouroccasionalvisitstothispartofSouthAmerica，weheardofaship，twochurches，andahousehavingbeenstruck。BoththechurchandthehouseIsawshortlyafterwards：
thehousebelongedtoMr。Hood，theconsul-generalatMonteVideo。Someoftheeffectswerecurious：thepaper，fornearlyafootoneachsideofthelinewherethebell-wireshadrun，wasblackened。Themetalhadbeenfused，andalthoughtheroomwasaboutfifteenfeethigh，theglobules，droppingonthechairsandfurniture，haddrilledinthemachainofminuteholes。Apartofthewallwasshattered，asifbygunpowder，andthefragmentshadbeenblownoffwithforcesufficienttodentthewallontheoppositesideoftheroom。Theframeofalooking-glasswasblackened，andthegildingmusthavebeenvolatilized，forasmelling-bottle，whichstoodonthechimney-piece，wascoatedwithbrightmetallicparticles，whichadheredasfirmlyasiftheyhadbeenenamelled。[1]Hearne’sJourney，p。383。
[2]Maclaren，art。“America。”Encyclop。Brittann。
[3]Azarasays，“Jecroisquelaquantiteannuelledespluiesest，danstoutescescontrees，plusconsiderablequ’enEspagne。”
[4]InSouthAmericaIcollectedaltogethertwenty-sevenspeciesofmice，andthirteenmoreareknownfromtheworksofAzaraandotherauthors。ThosecollectedbymyselfhavebeennamedanddescribedbyMr。WaterhouseatthemeetingsoftheZoologicalSociety。ImustbeallowedtotakethisopportunityofreturningmycordialthankstoMr。
Waterhouse，andtotheothergentlemanattachedtothatSociety，fortheirkindandmostliberalassistanceonalloccasions。
[5]InthestomachandduodenumofacapybarawhichIopenedIfoundaverylargequantityofathinyellowishfluid，inwhichscarcelyafibrecouldbedistinguished。Mr。Oweninformsmethatapartoftheoesophagusissoconstructedthatnothingmuchlargerthanacrowquillcanbepasseddown。Certainlythebroadteethandstrongjawsofthisanimalarewellfittedtogrindintopulptheaquaticplantsonwhichitfeeds。
AttheR。Negro，inNorthernPatagonia，thereisananimalofthesamehabits，andprobablyacloselyalliedspecies，butwhichIneversaw。ItsnoiseisdifferentfromthatoftheMaldonadokind；itisrepeatedonlytwiceinsteadofthreeorfourtimes，andismoredistinctandsonorous；whenheardfromadistanceitsocloselyresemblesthesoundmadeincuttingdownasmalltreewithanaxe，thatIhavesometimesremainedindoubtconcerningit。
Geolog。Transact。vol。ii。p。528。InthePhilosoph。Transact。1790，p。294Dr。Priestlyhasdescribedsomeimperfectsiliceoustubesandameltedpebbleofquartz，foundindiggingintotheground，underatree，whereamanhadbeenkilledbylightning。
[Azara’sVoyage，vol。i。p。36。PreviousChapterNextChapterTheVoyageoftheBeagle-Chapter4TheVoyageoftheBeaglebyCharlesDarwinPreviousChapterNextChapterChapter4-RioNegrotoBahiaBlancaJULY24th，1833——TheBeaglesailedfromMaldonado，andonAugustthe3rdshearrivedoffthemouthoftheRioNegro。ThisistheprincipalriveronthewholelineofcoastbetweentheStraitofMagellanandthePlata。ItenterstheseaaboutthreehundredmilessouthoftheestuaryofthePlata。Aboutfiftyyearsago，undertheoldSpanishgovernment，asmallcolonywasestablishedhere；anditisstillthemostsouthernpositionlat。41degs。onthiseasterncoastofAmericainhabitedbycivilizedman。
Thecountrynearthemouthoftheriveriswretchedintheextreme：
onthesouthsidealonglineofperpendicularcliffscommences，whichexposesasectionofthegeologicalnatureofthecountry。Thestrataareofsandstone，andonelayerwasremarkablefrombeingcomposedofafirmly-
cementedconglomerateofpumicepebbles，whichmusthavetravelledmorethanfourhundredmiles，fromtheAndes。Thesurfaceiseverywherecoveredupbyathickbedofgravel，whichextendsfarandwideovertheopenplain。
Waterisextremelyscarce，and，wherefound，isalmostinvariablybrackish。